AU776501B2

AU776501B2 - Water-resistant plaster-based prefabricated construction element

Info

Publication number: AU776501B2
Application number: AU24458/00A
Authority: AU
Inventors: Regis Humbert; Daniel Martin; Theo Theuvsen
Original assignee: Lafarge Platres SA
Current assignee: Etex France Building Performance SA
Priority date: 1999-02-12
Filing date: 2000-02-07
Publication date: 2004-09-09
Anticipated expiration: 2020-02-07
Also published as: HK1041872A1; DE60016572T2; FR2789679B1; BR0008142A; FR2789679A1; EP1152997A1; EP1152997B1; ZA200105631B; KR20020034987A; WO2000047536A1; AU2445800A; TR200102344T2; CA2361711C; CN1246247C; KR100713034B1; PL350319A1; ID30289A; JP2002539061A; CA2361711A1; DE60016572D1

Description

WATER RESISTANCE PLASTER-BASED PREFABRICATED CONSTRUCTION

ELEMENT

The present invention relates to prefabricated structural elements comprising a substrate based on cured and dried plaster. More particularly, the invention relates to prefabricated structural elements of the tile, panel and board types. With regard to boards, those relevant to the present invention have a relatively small average thickness, for example ranging from one to a few centimeters, in a preferred direction or dimension, with a limited mass per unit area, for example about kilograms per m 2 By way of preferred but nonlimiting example, reference will be made to prefabricated elements of the board type, in the knowledge that at the present time there are, for example, plaster fiberboards in which the plaster contains homogeneously dispersed fibers throughout the mass, these boards being commonly called "GFBs", and plasterboards coated with cardboard or with mats or sheets of mineral fibers (for example glass fibers) on both their faces.

o 15 The present application corresponds to French Patent Application o• No. 99/01885 of 12.02.1999, the text of which is incorporated in that of the present Si'" patent application, as required.

In this specification, where a document, act or item of knowledge is referred to or Sdiscussed, this reference or discussion is not an admission that the document, act or item of 20 knowledge or any combination thereof was at the priority date: o •o S part of common general knowledge; or oooo (ii) known to be relevant to an attempt to solve any problem with which this specification o is concerned.

The invention applies to other prefabricated elements made of plaster, for 25 example to tiles, or parallelepipedal elements having grooves or slots and tenons on their side edges.

The invention relates to prefabricated structural elements, such as those defined above, having improved water resistance.

The prefabricated structural elements as defined above, having the ability to withstand water, are used either inside buildings, for example in humid rooms such as bathrooms, in order to lay plastic coverings or tiles thereon, or on the outside of tvlm M0111546037v3 304670404 buildings, for example for the covering of falades, as long as, nevertheless, these prefabricated elements are coated with an impermeable protective skin.

The expression "water resistant" should be understood to mean the ability of a prefabricated structural element as defined above to limit the uptake of water by the plaster substrate, while still retaining the dimensional stability and mechanical integrity of the structural element in question.

Depending on the countries, this water resistance is codified or regulated by specific standards. Thus, reference may be made to the standards mentioned below, depending on the element manufactured: plaster tile: NF P72-210-1 (April 1994); plasterboard: ASTM 630/630M-96a; board with a glass mat: ASTM Cl 178/1178M (96).

The ASTM 630/630M-96a standard requires in particular that, when such a S•"structural element is immersed in water for two hours, the water uptake by the Cobb equivalent) is less than 160 g/m 2 •For the purposes of making a structural element, as defined above, water-repellent in accordance with document JP-A-0 730 411, it is known to use a water-repellent agent comprising at least one silicone compound in aqueous and basic medium and to homogeneously incorporate the latter into the substrate of the element in question.

According to JP-A-0 733 0411 the silicone compound is emulsified with Swater. An oxide or hydroxide of a metal from group Ila, for example calcium, is then added to the emulsion. The additive thus obtained is then incorporated into the dry matter in order to obtain the plaster substrate in the wet state, which substrate is then formed and then dried.

In practice, it appears that the aforementioned composition has the advantage of causing the silicone compound to cure or crosslink, thereby enhancing the water-repellency of the latter; however, this is accompanied by significant evolution of hydrogen, which is particularly dangerous.

tvlm M0111546037v3 304670404 Document JP-A-80109251 discloses a water-repellent composition for cement, comprising a silicone compound, the nature of which is not specified, and bentonite as mineral additive.

Document SU-A-1409607 discloses a water-repellent composition for plaster, comprising a sodium methyl siliconate or ethyl siliconate, and bentonite as mineral additive.

In practice, such a composition is able to swell, causing rheological problems of the substrate in the slurry state.

It appears in practice to be difficult to meet the abovementioned standards using contents of silicone compound of less than 1% by weight, said compound being, moreover, very costly.

This water repellency is achieved by using any process comprising, in general, at least the following steps: homogeneously mixing a dry material, comprising mostly at least one 15 hydratable calcium sulfate, the abovementioned water-repellent agent, and water and preforming said substrate in the wet state; :i drying the preformed substrate in order to obtain said substrate formed in the solid and dry state.

With such a process, it is difficult to control the amount of water-repellent agent incorporated into the plaster substrate, for example in the form of a silicone oil, and therefore the potential of the water-repellent agent is not exploited.

The object of the present invention is therefore to better control the water repellency of a structural element using a water-repellent agent comprising at least one silicone compound, in particular to increase its water repellency within the cured plaster.

The object of the present invention is also to improve the introduction and mixing of the water-repellent agent in the process defined above.

In accordance with the present invention, it has been discovered that the addition, as a homogeneous mix, of a mineral additive comprising at least one tvlm M0111546037v3 304670404 mineral component having a synergistic water-repellency affinity with the silicone compound to the dry matter from which the substrate is preformed in the liquid state allowed the water repellency of the cured plaster to be increased to a significant extent.

The expression "synergistic water-repellency affinity" should be understood to mean the property whereby, by adding the mineral additive according to the present invention, and all other things being equal, the water repellency of the cured-plaster substrate is increased by at least 20%, in Cobb equivalent, according to the ASTM 630/630M-96a standard, and/or, for the same water resistance, the amount of water-repellent agent required is reduced by at least Preferably, but nonlimitingly, the mineral component does not react with the silicone compound in the sense that, after two hours, mixing 0.1 g of said silicone compound with the mineral component in aqueous medium may release an amount of hydrogen of less than or equal to 6 ml under standard temperature and pressure conditions.

The evolution of hydrogen is measured according to the following operating method.

oooo :An apparatus identical to that described in the NFT 77-150 standard on page 6 is used. The principle consists in bringing the mineral additive and the silicone 20 compound into contact with each other, in aqueous medium in the reactor, in the same proportions by weight as those in the homogeneous mix defined above, in the slurry state, that is to say with the mixing water. The evolution of hydrogen is monitored over time, at a controlled temperature of 23°C. The volume of hydrogen evolved after two hours is noted.

o 25 A mineral component that hardly reacts at all with the silicone compound is one which produces a parasitic evolution of hydrogen, after two hours, of less than or equal to 6 ml under standard temperature and pressure conditions.

A mineral additive according to the invention therefore makes it possible to increase the water resistance of a structural element according to the invention and/or to reduce the amount of water-repellent agent required for a predetermined level of water resistance.

lm M0111546037v3 304670404 According to the present invention, with regard to a crystalline mineral component containing a hydroxyl functional group which is nonionizable in an aqueous medium, one possible explanation (among other hypotheses) for the observed synergy, supported by the experimental protocol described below, is the formation of at least one hydrogen bond, in neutral or acid aqueous medium, between, on one side, the hydrogen of a nonionizable hydroxyl functional group of the mineral component and, on the other side the oxygen of the silicone compound.

In other words, according to the invention, the mineral component adsorbs the silicone compound. Furthermore, the homogeneous mixing of the mineral additive into the plaster substrate allows the homogeneous distribution and the fixation of the silicone compound.

During the curing, the hydroxyl ions naturally present in the aqueous medium may bring about three-dimensional crosslinking of the silicone compound, this being manifested by an improvement in the water-repellency properties of the cured 15 plaster over time.

Consequently, the adsorption of the silicone compound on the mineral component makes it possible to control its reactivity, that is to say to delay the latter :until the moment of curing the plaster.

Preferably, according to the invention, the reactive silicone compound is a 20 linear, cyclized or branched macromolecular water-repellent compound containing polysiloxane units, each of which is chosen from the group consisting of the groups (RiR 2

R

3

(RR

2 SiO) and (R 2 SiO 3 with: R, H, Cl, or any other halogen, or an alkoxy

R

2 a branched or unbranched phenyl or alkyl R a branched or unbranched phenyl or alkyl.

By way of example, the silicone is an alkyl hydrogenopolysiloxane, such as methyl hydrogenopoly-siloxane, in the form of an oligomer (several tens or more of siloxane units), in the form of an oil or of an aqueous emulsion.

Preferably, according to the invention, the reactive mineral component is a crystalline mineral material which contains a hydroxyl functional group i which is rvim M0111546037v3 304670404 nonionizable in aqueous medium, for example a clayey material and/or a crystalline silica.

As an example of such a crystalline mineral material, mention may be made of a clayey material, preferably one which does not swell in aqueous medium (unlike pentonite), comprising especially an aluminosilicate, for example an illite and/or a kaolin.

A mineral additive according to the invention optionally comprises an inert mineral component.

In accordance with the invention, the mineral additive is inert with respect to calcium sulfate, initially in powder form. It comprises, for example, a clayey material, as mentioned above.

By virtue of the invention, and when a papermaking-type process is used, especially by filtration of a slurry, to manufacture GFB boards based on cellulose fibers, it has been found that the incorporation of a mineral additive comprising, for 15 example, a clayey material made it possible to retain the water-repellent agent within the plaster substrate preformed in the wet state. This makes it possible to increase, for the same content of water-repellent agent, the water resistance of the GFB boards manufactured by such a process, and in particular to limit the amount of this agent in the recycled water of hydration.

20 The present invention also has the following secondary features: the composition by weight of the mineral additive in the dry matter, in combination with the amount and nature of the water-repellent agent, is tailored to give the cured-plaster structural element a water resistance which meets the aforementioned standards, and in particular the ASTM 630/630M-96a standard, for a so-called GFB board; the reactive silicone compound represents a proportion by weight of the total dry matter introduced of at least 0.1% and preferably between 0.1 and 1%; tvlm M0111546037v3 304670404 the reinforcing fibers, for example cellulose fibers, are distributed in the cured-plaster substrate; the structural element is, for example, a so-called GFB fiberboard; the element has the shape of a board and the two faces of the cured-plaster substrate are coated with two sheets of cellulose fibers, for example with cardboard; the mineral additive has a particle size distribution such that the particles having a size of less than or equal to 63 um represent a proportion by weight of at least 85% of said mineral additive; preferably, the mineral additive has a loss on ignition at 900'C of less than 30%; by way of example, the mineral additive has a loss on ignition of less than 30%; by way of example, the mineral additive represents a proportion of the total weight of the ingredients, excluding water of hydration, of at least 5% and preferably at most 15 the hydratable calcium sulfate is obtained from a natural gypsum or *O*o from a sulfogypsum, the latter coming from the desulfurization of gases ~from thermal power stations; the reactive silicone compound may be introduced during the manufacture of the structural element, in the form of an emulsified :.20 composition of a silicone in water; "by way of example, in combination, the mineral additive comprises a clayey material, a crystalline silica and, optionally, an inert mineral supplement compatible with the clayey material and dispersible in the cured-plaster substrate; the composition by weight of the mineral additive is tailored, in conjunction with the water-repellent agent, also to give the structural element, used in wall partitions, a fire resistance which meets the so-called "GKF" standards according to DIN 18180 and 4102 (part IV); the inert mineral supplement, if it is present in the mineral additive, is, for example, dolomite and the mineral additive then comprises, in approximately equal proportions by weight, the clayey material tlm M0111546037v3 304670404 (including the crystalline silica) and the inert mineral supplement; this particular mineral additive makes it possible, with the water-repellent agent, to obtain boards which are both fire resistant and water resistant and which in particular meet both the GKF standards and the aforementioned water-resistance standards, whatever the process used to obtain the plasterboards or to obtain so-called "GFB" fiberboards; reinforcing fibers, preferably mineral fibers compatible with the hydratable calcium sulfate, for example glass fibers, are also distributed in the cured-plaster substrate in a proportion by weight with respect to the total of the dry matter introduced of less than 1% when it is desired, in particular, to improve the fire resistance of the boards; by way of another example, the mineral additive comprises an amorphous silica and/or diatomaceous earth and/or ferrite and/or a zeolite; 15 more generally, the mineral additive according to the invention 0 comprises a mineral component having an affinity with respect to the silicone compound, finely ground (for example 1 jm), taken from clays; smectites are preferred, then illites and kaolinites; the structural element according to the invention has a shape chosen 20 from the group consisting of tiles, panels and boards.

The present invention also relates to a water-repellent composition comprising, as homogeneous mix, a water-repellent agent comprising a silicone compound and a mineral additive comprising at least one mineral component having a synergistic water-repellency affinity with said silicone compound, as defined above.

0* The invention also relates to the use of this composition within a plaster substrate of a prefabricated structural element.

The invention also relates to the use of a mineral additive to increase the water repellency of a water-repellent agent comprising a silicone compound.

According to the invention, the mineral additive comprises at least one mineral component having a synergistic water-repellency affinity with said silicone compound, as defined above.

tvlm M0111546037v3 304670404 The invention also relates to a process for manufacturing a structural element comprising a substrate based on cured plaster, in which said substrate is obtained by at least the following steps: a) dry matter comprising mostly at least one hydratable calcium sulfate, a water-repellent agent comprising at least one silicone compound and water of hydration are mixed homogeneously and said substrate is preformed in the wet state; b) the preformed substrate is dried in order to obtain the substrate formed in the solid and dry state.

According to the invention, during step a mineral additive, comprising at least one mineral component having a synergistic water-repellency affinity with said silicone compound, as defined above, is also mixed.

Preferably, the ingredients defined in step are mixed directly and together, in order to obtain the substrate in the wet and preformed state.

Such a process may have the following variants: the water-repellent agent is in liquid form, particularly in the form of an o# oil, or of a homogeneous aqueous suspension, while the mineral additive is a powder in divided form; the water-repellent agent is mixed homogeneously with the dry matter 20 comprising the mineral additive, before said dry matter is mixed with the water of hydration, in order to obtain the substrate preformed in the wet state; the water-repellent agent is mixed homogeneously with the water of hydration, before the latter is mixed with the dry matter comprising the •go° 0::25 mineral additive, in order to obtain the substrate preformed in the wet state; the water-repellent agent and the mineral additive are mixed homogeneously in order to obtain a powder imbibed with oil on the surface, which powder is then incorporated into the dry matter and/or tvlm M0111546037v3 304670404 the mixing water before they are homogeneously mixed, in order to obtain the substrate preformed in the wet state; the water-repellent agent, in the form of an oil or an aqueous emulsion, is homogeneously dispersed in the mixing water, whereas the mineral additive is distributed homogeneously in the dry matter.

According to the present invention, it has been discovered that if the homogeneous mixing of the above-defined ingredients, prior to the preforming of the substrate in the wet state, also includes a mineral additive as defined above, and in particular a clayey material, then this mineral additive is able to act as a retention agent for the reactive silicone compound within the plaster-based substrate.

The solution according to the invention has the major advantage of remaining compatible with the various processes known at the present time for manufacturing the structural elements considered by the present invention, for example: by casting a plaster-based slurry between two sheets of cellulose fibers, in the form of cardboard, or between two mats, wovens or sheets of mineral fibers; by filtering a slurry based on cellulose fibers and on plaster, using a papermaking-type process, in order to obtain so-called GFB fiberboards; o 20 by so-called semi-wet or semi-dry compression, depending on the water content (GFB fiberboards).

Applied to each of these processes, the invention makes it possible to increase the efficiency of incorporation of the water-repellent agent within the plaster substrate. For example, for a process involving the filtration of a slurry, of the S: 25 papermaking type, the invention makes it possible to keep the water-repellent agent S within the cake obtained by filtration, rather than concentrate it in the filtrate, despite recycling the water of hydration.

Throughout the description below, the term "cured plaster" or "plaster" will be reserved for calcium sulfate dihydrate (CaSO 4 .2H 2 0) or regenerated gypsum.

tlm M0111546037v3 304670404 The term "hydratable calcium sulfate" should be understood to mean a mineral compound or a composition consisting of or comprising an anhydrous calcium sulfate (anhydrite II or III), a calcium sulfate hemihydrate (CaSO 4 1 2

H

2

O),

whether in the crystalline a or P form of the latter.

The term "silicone compound" should be understood to mean any compound capable of being obtained by the polymerization of a silicone-type monomer unit, whether this is, for example, a chlorosilane, a siliconate, an alkoxysilane or a silanol.

The term "cellulose fibers" should be understood to mean discrete elements such as fibers, filaments and chips, based on natural, regenerated, recycled or modified cellulose; preferably, the cellulose fibers in question are those generally used in the composition of papers and cardboards.

The term "mineral fibers" should be understood to mean inorganic fibers, for example glass fibers, which may or may not be treated in order to remain chemically stable and inert once they have been incorporated into the cured-plaster substrate of the prefabricated structural elements considered by the present invention.

As is known, dolomite is a mixed calcium and magnesium carbonate.

Throughout the present invention, unless otherwise specified, all the compositions are expressed with respect to the total weight of the dry matter introduced, including the water-repellent agent. These compositions may be easily 20 transposed with respect to the final weight of the prefabricated, finished and dry structural element, taking into account the water of rehydration of the calcium sulfate.

According to the present invention, the mineral additive used does not o* develop by itself, in aqueous medium, an alkaline pH. This excludes as mineral 25 component any material capable of releasing, in aqueous medium, OH ions, for example: a) a mineral base, such as calcium dihydroxide; or b) a metal silicate, for example containing no hydroxyl ions, for example a calcium silicate, such as that sold by Lafarge under the reference CPA 52,5 CP2; or tvlm M0111546037v3 304670404 c) an aluminate, for example a calcium aluminate, such as that sold by Lafarge under the reference SECAR In this regard, reference will be made to Figure 1, which shows the evolution of hydrogen (at atmospheric pressure and at 23 0 C) for three mixes according to the following representation: the solid line corresponds to a mix comprising 0.1 g of Ca(OH) 2 0.1 g of MHPS (BS94 from Wacker) 65 ml of water; the dotted line corresponds to a mix comprising 1.72 g of a calcium silicate (the abovementioned commercial ref.) 0.1 g of MHPS (BS94 from Wacker) 65 ml of water; the dot-dash line corresponds to a mix comprising 1.72 g of a calcium aluminate (the abovementioned commercial ref.) 0.1 g of MHPS (BS94 from Wacker) 65 ml of water.

The volume expressed in ml is plotted on the x-axis and the contacting time, in hours, is plotted on the y-axis.

This is because it is sufficient to mix any of the aforementioned mineral components to with a reactive silicone compound, for example methyl hydrogenopolysiloxane (abbreviated to MHPS), in aqueous medium, to immediately observe a violent and abundant evolution of hydrogen.

o* 20 As indicated previously, a reactive mineral component of the bentonite type appears to be excluded for the manufacture of certain structural elements comprising a substrate based on cured plaster, such as plasterboards.

EXAMPLE 1: The example given below illustrates, in the case of plasterboards, the problem 25 of spreading the substrate, or slurry, in the wet state, the problem of bonding between the cured-plaster substrate and the sheets of cellulose fibers or cardboard, and the problem of longer drying time, problems which are generated by the use of bentonite.

Operating method: tvlm M0111546037v3 304670404 13 Boards were manufactured on a laboratory production line, by casting between two cardboard sheets, and drying using the appropriate drying profile without calcining the cured plaster.

The water-repellent agent used is in the form of a silicone oil (MHPS) (Wacker BS 94).

The following measurements were made throughout the manufacturing process: Spread: measurement in millimeters in two directions perpendicular to the diameter of a disk, after being spread over a glass plate. The disk is obtained by vertically lifting a cylindrical mold having an internal diameter of 60 mm 0.1 mm and a height of [lacuna] 0.1 mm, filled with the plasterboard slurry. The time taken to lift the mold is identical to that for casting the slurry between the two cardboard sheets.

Shear bonding: this is the time needed for the crystallization of the set plaster to be characterized by adhesion to the paper during a peel test.

This bonding must be sufficient to enable a plasterboard to be introduced into an industrial dryer without the risk of debonding from o the cardboard.

Drying time: the time needed to reach at least 0.2% moisture inside the -20 boards dried according to the appropriate profile, without calcining the ~cured plaster.

.Dry bonding: in a peel test of a board containing less than 0.2% moisture, the quality of the bond between the set plaster and the paper must be perfect and leave no trace of set plaster visible. In the case of poor bonding, the measurement is expressed as the amount of set plaster visible.

The results obtained are given in Table A below.

vlm M0111546037v3 304670404 TABLE A Mineral Amount Spread Sheer Drying Dry additive of (mm) bonding time bonding mineral (min) (min) of set additive plaster visible) RG1842 none 180 7 49 0 RG1843 113 194 8 49 0 RG1844 bentonit 113 110 >12 69 56 e composition A of Table 1 below.

9 9.

9 9*9* 9 9 .9 9* EXAMPLE 2: For the manufacture of so-called GFB boards, of 1.1 density, the filterability of three slurries was tested under a vacuum of 0.2 bar, these slurries being obtained by mixing, respectively: 1) 133 g of hydratable calcium sulfate (semihydrate); 12 g of dry pulp and 388 g of water; 2) 133 g of hydratable calcium sulfate (sulfogypsum), 12 g of dry pulp, 15.78 g of a nonswelling clayey material of composition X from Table 1 below and 388 g of water; 3) 133 g of hydratable calcium sulfate (sulfogypsum), 12 g of dry pulp, 15.78 g of bentonite and 388 g of water.

The filterability of the slurry, having a density of 1.1, under a vacuum of 0.2 bar, is shown by the graph in Figure 2, in which the volume of the filtrate expressed in ml is plotted on the y-axis and the filtration time expressed in seconds is plotted on the x-axis. The following correspondence table should be noted: the solid line corresponds to the slurry according to the dot-dash line corresponds to the slurry according to and tvlm M0111546037v3 304670404 the dotted line to the slurry according to Whatever the filtration time, the volume of water recovered in the case of mix is much less than that recovered in the case of mixes and these being of the same order of magnitude for both and Thus, after 20 s, only 80 ml of water are recovered from mix compared with 110 and 120 ml in the case of mixes and respectively.

EXAMPLE 3: This example is particularly important in that it shows, firstly, the chemical reaction existing between an MHPS and a conventional mineral additive and, secondly, the absence of a chemical reaction existing between the same MHPS and a clayey material.

For this purpose, 0.1 g of MHPS (reference BS94 from Wacker), in 85 ml of water, are mixed, respectively, with 0.1 g of Ca(OH) 2 and 1.8 g of a clayey material, namely composition X according to Table 1.

A continuous evolution of hydrogen is obtained in the first case, while in the second case there is no evolution of hydrogen, in accordance with the graph in oFigure 1.

This is illustrated in Figure 3 with the same conventions as in Figure 1.

The solid line represents the evolution of hydrogen in the first mix and the 20 dot-dash line the evolution in the second mix.

The formulations of the mineral-additive compositions and are given in Table 1 below, in percentages by weight.

o o

*J~

o *o o• tvim M0111546037v3 304670404 16 TABLE 1 Composition X 1 Composition Z Mineralogical composition1

M%

Kaolin 25 Illte 10 Quartz 15 Dolomite 50 0 Calcined chemical composition(% S'0 2 43 72.4 T'0 2 1.1 1.6 A1 2 0 3 15 21.5 Fe.0 3 1.6 1K20 1.2 2.1 GaO 23 0.2 MgO 14 0.3 Particle size distribution 63 j.m screen oversize 15% 1.7% Loss on ignition at 900'C 26.5% 5.7% EXAMPLE 4: Water-repellency of cured plasterboards with methyl hydrogenopolysiloxanes in the form of oils.

S S S S

S.

S S S S S. S 55

S

*SS

S

SS*S

55 S S

S

S S 5* S S*

S.

S

tvm MO0I1I1546037v3 304670404 4.1/ GFB fiberboards (cellulose fibers) with and without filtration 4.1.1/ Heavy GFB fiberboards obtained with filtration according to a "papermaking" process.

The board is manufactured according to the following successive steps: Preparation of a pulp, by mixing 8 liters of water (tap water or water coming from the recycling of the filtrate from boards of the same formulation) with 273 g of newsprint, followed by pulping using a RAYNERI® mixer, Turbotest 207370 model, for 20 minutes at speed 6 and then for 25 minutes at speed Weighing a 2400 g quantity of pulp in a HOBART® bowl, N-50G model, i.e.

approximately 2321 g of water and 79 g of dry pulp.

Introduction of a variable amount, depending on the trials (see Table of methyl hydrogeno-polysiloxane of reference 1107 from Dow Chemical or reference from Bayer.

Weighing, into a separate container, an 800 g quantity of hydratable calcium sulfate (CaSO 4 2

H

2 obtained by the curing of a natural gypsum or of a sulfogypsum coming from the desulfurization of flue gases.

0 Introduction into this hydratable calcium sulfate, and mixing using a suitable mechanical means, a variable amount of mineral additive of composition or depending on the trials (see Table 2).

*0 0 20 Introduction of the hydratable calcium sulfate, to which the above additive has been added, into the HOBART® bowl and mixing at speed 1 for 15 seconds with an N5B NSF blade. Scraping for 15 seconds and mixing at speed 1 for 90 seconds.

Deposition of the plaster suspension thus obtained in a mold provided with a permeable cloth, of dimensions 25.5 x 25.5 cm 2 or 60 x 40 cm 2 depending on the i: 25 size of the board desired.

Mechanical pressing until a cake approximately 12.5 mm in thickness is obtained.

Application of pressure for at least 20 seconds in order to expel the air and water through the filtration cloth.

tvlm M0111546037v3 304670404 18 Demolding.

Standing at room temperature until complete dehydration of the hydratable calcium sulfate.

Drying the plaster with a suitable temperature profile, without calcining the cured plaster.

Table 2 below summarizes the characteristics of the GFB boards having a thickness of approximately 12.5 mm, these being manufactured using this protocol in a mold of dimensions 25.5 x 25.5 cm 2 o** e o e go* tvlm M0111546037v3 304670404 S P 5 S S S S 55555 *5 S S P SSSS S. 55 5 S 19 TABLE 2 Mirera additivecaliu Dry matter in Water-repellent agent Total dry Ta watertWate No. sulfate Miea diie the pulp (silicone oil) weight TpwtrWer density Water/ Total dry Weight weigh Type Type M% M% Type M% t M% 1 S 800 91 -79 9 0.00 879 2321 2.64 29.0 1.16 2 S 800 91 -79 9 -0.00 879 2321 2.64 25.0 1.19 3 S 800 90.5 -79 9 DC 5 0.5 884 2321 2.62 27.0 1.17 4 S 800 90 -79 9 DC 10 1.0 889 2321 2.61 19.0 1.19 S 800 81.5 Z 100 10 79 8 DC 5 0.5 984 2321 2.36 5.0 1.12 6 N 800 81.5 X 100 10 79 8 MH 3 0.5 982 2321 2.36 3.1 118 S: sulfogypsum N: natural gypsum DC: Dow Chemical 1107 silicone oil MH: Bayer MH15 silicone oil tvIm M0111546037v3 304670404 The percentage water uptake after 2 hours is measured according to the ASTM 630/630M-96a standard, but on specimens of dimensions 10 x 10 cm 2 when the standard recommends specimens of one square foot. The results obtained according to this protocol are less favourable than the results that would have been obtained using specimens of dimensions according to the standard.

Trials 1 and 2 are controls: the boards containing no water-repellent have high percentages of water uptake. It is found that when no mineral additive is used (Trials 3 and the water-repellency results are not good, even when a water-repellent agent is present. On the other hand, as soon as a mineral additive according to the invention is used, very much lower water uptakes are obtained, in accordance with the standard.

4.1.2 Light GFB fiberboards (cellulose fibers) obtained with filtration using a papermaking process The board is manufactured according to the following successive steps: 15 Preparation of a pulp, by mixing 8 liters of water (tap water or water coming from the recycling of the filter [sic] from boards of the same formulation) with 273 g of newsprint, followed by pulping using a Rayneri mixer, Turbotest 207370 model, for 20 minutes at speed 5 and then for 25 minutes at speed Weighing of a 2083.5 g amount of pulp in a Hobart bowl, N-50G model, i.e.

approximately 2021 g of water and 62.5 g of dry pulp.

Introduction of 2.7 g of methyl hydrogeno-polysiloxane of reference BS94 from Wacker and mixing for 2 minuets.

Introduction of a 53.4 g amount of additive X (cf. Table 1) and mixing for minutes.

Weighing, into a separate container, of a 250 g amount of hydratable calcium sulfate (CaSO 4

H

2 0O) obtained by the curing of a natural gypsum or of a sulfogypsum coming from the desulfurization of flue gases.

tvlm M0111546037v3 304670404 Introduction of the calcium sulfate into the Hobart bowl and mixing at speed 1 for 15 seconds using an N5B NSF blade. Scraping for 15 seconds and mixing at speed 1 for 90 seconds.

Trials 1 and 2 are controls: the boards containing no water-repellent agent have high percentage water uptakes. It may be seen that when a mineral additive is not used (Trials 3 and the water-repellency results are not good, even in the presence of a water-repellent agent. On the other hand, as soon as a mineral additive according to the invention is used, very low water uptakes are obtained, in accordance with the standard.

The following results are obtained, as in Table 3.

tvlm M0111546037v3 304670404 *9 99 9 9 9 99 .9 9 9 9 9 9 9. 9 9 9 9 9 99999 9. 9 9* 99 *9 99 9 9 9. 9 999 22 9 TABLE 3 Tra yrtbe Mineral additive Dry Wae-eelet Ttl)r a No. calcium sulfate Dry matter in matter in Wa-epent Toita dr wape Density Water the pulp [sic] the pulp uptake Type Type 5GI [sic] M% 1S 250 62.5 312.5 2021 0.45 147 MP97 S 250 62.5 BS94 2.7 315.2 2021 0.40 119 MP9907 S 250 :c 53.4 62.5 BS94 2.7 369 2021 0.45 4.8 8 *Composition X according to Table 1 tvlm MO111546O37v3 304670404 4.2 Manufacture of GFB fiberboards (cellulose fibers) by compression using a semi-wet or semi-dry process The board is manufactured according to the following steps: Preparation of a paper fluff by grinding newsprint in a Pallman-type apparatus.

Weighing of a quantity of fluff and introduction into a Lodige of the or M5G type.

Weighing of a variable quantity of mineral additive of formula Z or X, depending on the trials.

Spraying of methyl hydrogenopolysiloxane onto the mineral additive.

Introduction of the mix obtained into the Lodige of M20G.RE or MSG [sic] type and mixing so as to obtain a homogeneous mix.

Weighing, into a separate container, of a quantity of natural hydratable calcium sulfate or a hydratable calcium sulfate coming from the 15 desulfurization of flue gases.

Introduction of this hydratable calcium sulfate into the Lodige of or M5G type and mixing so as to make a homogeneous mix.

Deposition of the above homogeneous mix into a mold of dimensions 40 x CM2 and spraying a quantity of water.

20 Pressing using a 50-tonne KRATOS-type press with a separate pump of reference PKPS until a 12.5 mm thick cake is obtained.

C. Application of the pressure for at least 20 seconds in order to expel the water through the drainage cloth, which is placed in the lower part of the mold.

Demolding.

Standing at room temperature for at most 1 hour 30 minutes until the plaster is completely hydrated.

tvlm M0111546037v3 304670404 24 SDrying with a suitable temperature profile without calcining the set plaster.

Comment: In the case of the manufacture of a board without a mineral additive, the methyl hydrogenopolysiloxane is introduced into the water.

The table below summarizes the characteristics of the approximately 13 mm thick panels manufactured using this protocol in a mold of dimensions 40 x 40 cm 2 TABLE 3A Water-repellent Water Trial Hydratable Mineral additive agent Total Tap Water Uptake No. calcium sulfate (silicone Weight after oil) 2h Water/ Weight dry Type Type Type (g) weight ratio 1 S 1993 2430 1380 0.57 30.5 2 S 1993 MH 13 2006 1380 0.56 13 S 1886 X 130 MH 13 2443 1380 0.56 2 The water uptake after 2 hours is measured as previously.

It is found that the water uptake results are better when the boards are 0 manufactured with a water-repellent agent and a mineral additive, both in accordance with the invention.

a a a a. a a.

a a tvlm M0111546037v3 304670404 4.3 So-called GKF plasterboards Boards called GKFs because of their fire resistance, that is to say boards which comprise a cured-plaster substrate whose faces are coated with a cardboard, were manufactured on an industrial production line by casting plaster between two cardboard sheets. The water-repellent agent used is in the form of silicone oil (Wacker BS94).

The following results are obtained, according to Table 4.

Table 4 Silicone Mineral additive Water uptake compound* in in of the after 2 h of the weight of final weight of immersion on the finished the board 30x30 cm board specimens 0.42% 0% 16.8% 0.36 3.72% 0.36 7.18% 4.25% Commercial reference WACKER® BS94 0 4.4 Manufacture of water-repelled reinforced molded elements obtained by dry compression, using various ways of introducing the water-repellent agent This example illustrates the manufacture of test pieces of dimensions 2 x 2 x 18 cm, during which a silicone oil is applied to various supports, so as to make a cured-plaster element water-repellent, with or without fibers.

C

C C C C

C

CC C

C

The following products and conditions were used: Dry matter: Hydratable calcium sulfate: plaster coming from the curing of a natural gypsum, having a pH of 7.22 measured as a 10% suspension after stirring for minutes.

tvlm M0111546037v3 304670404 Mineral additive: Composition X or Z Silica C400 quartz from Sifraco Dolomite from Lhoist Cellulose fibers identical to those in Example 1.2.

Silicone compound: silicone oil (methyl hydrogenopolysiloxane) in oligomeric form containing approximately 40 units, sold under the name MH150® by Bayer.

Operating conditions: Spraying of the silicone oil onto the water-repellency support, namely the hydratable calcium sulfate, or the mineral additive, or the cellulose fibers. The silicone compound is introduced in an amount of 0.5% of the weight of the total dry matter introduced. The quantity of water-repellency support varies depending on the trials. (cf. Table 15 Mixing for one minute in a HOBART mixer.

Mixing for 30 seconds with the water of hydration (the water of hydration/dry matter ratio is 0.6).

Filling of the mold.

Demolding after 30 minutes and then standing for 4 hours in a plastic bag.

20 Drying at 40*C until constant weight.

o Conditioning at 23 0 C and 50% RH.

The water uptake is measured, after immersion for 2 hours, on two test pieces in a manner identical to the conditions described in Example 1.1.

The water uptake results for the control and water-repelled test pieces according to the invention are given in Table 5 below.

When there are fibers or mineral additives, the quantities are expressed here as a percentage of the total dry matter introduced.

tvlm M0111546037v3 304670404 Table Mineral additive Cellulose fibers Water uptake after 2 h TS1 5.3 7.3 TS2 5.2 Z S 10 1.9 X S 10 4.4 C400 S 10 9.8 10.1 F S 5 22.5 22.8 D S 10 7.3 8.7 TS1 and TS2 are trials using test pieces made water-repellent using the same proportion of silicone compound introduced directly into the plaster suspension.

Z S: the silicone is sprayed onto the mineral additive of composition Z X S: the silicone is sprayed onto the mineral additive of composition X C400 S: the silicone is sprayed onto the C400 quartz mineral additive from Sifraco

S

S.

tvlm M0111546037v3 304670404 28 F S: he silicone is sprayed onto the cellulose reinforcing fibers D S: the silicone is sprayed onto the dolomite mineral additive.

It should also be noted here that the best results, with respect to the controls, are obtained when mineral additives of composition X and Z are used.

The word 'comprising' and forms of the word 'comprising' as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions which are obvious to the person skilled in the art and which do not have a material effect upon the invention.

S

0 0 0* *S 0**0* 00i0 o 0 :600, 0 i tvlm M0111546037v3 304670404

Claims

1. A water-resistant prefabricated structural element comprising a substrate based on cured plaster, the said substrate being able to be obtained by at least the following steps: homogeneously mixing a dry material, comprising mostly at least one hydratable calcium sulfate, a water-repellent agent comprising at least one silicone compound, and water and preforming the said substrate in the wet state; drying the preformed substrate in order to obtain the said substrate formed in the solid and dry state; characterized in that the homogeneous mix, prior to the preforming of the substrate in the wet state, also comprises a mineral additive comprising, on the one hand, a clayey material, which does not swell in aqueous medium and does not have a hydroxyl functional group ionizable in aqueous medium, and, 15 on the other hand, a crystalline silica, the said mineral additive, having a So: •synergistic water- repellency affinity with the said silicone compound, in the sense that, by virtue of adding the mineral additive to the homogeneous mix, O•* the water repellency of the substrate in the solid and dry state is increased by 'eve at least 20%, in equivalent Cobb, according to the ASTM 630/630M-96a standard, and/or for the same water repellency (or water resistance) the ."amount of water-repellent agent required is reduced by at least 04S*

2. The structural element according to Claim 1, characterized in that the clayey material hardly reacts at all with the silicone compound, in the sense that, 2after two hours, mixing of 0.1 g of the silicone compound with the said clayey o 25 material in aqueous medium, in the same proportions by weight as those used for the manufacture of the prefabricated structural element, may release an amount of hydrogen of less than or equal to 6 ml.

3. The structural element according to Claim 1 or Claim 2, characterized in that the silicone compound and the clayey material are able to form between them, tlm M0111546037v3 304670404 in acid or neutral medium, at least one hydrogen bond between, on one side, the hydrogen of a non-ionizable hydroxyl functional group of the clayey material and, on the other side, the oxygen of the silicone compound.

4. The structural element according to any one of Claims 1 to 3, characterized in that the clayey material comprises an aluminosilicate, for example an illite and/or a kaolin.

The structural element according to any one of Claims 1 to 4, characterized in that the mineral additive further comprises an inert mineral supplement compatible with the clayey material.

6. The structural element according to any one of Claims 1 to 5 characterized in that the silicone compound is a linear, cyclized or branched macromolecular water-repellent compound containing polysiloxane units, each of which is chosen from the group consisting of the groups (RiR 2 R 3 (RiR 2 SiO) and (R 2 Si03,), with: 15 R H, C1, or any other halogen, or an alkoxy S- R2 a branched or unbranched phenyl or alkyl S. R3 a branched or unbranched phenyl or alkyl.

7. The structural element according to any one of Claims 1 to 6, characterized in that the silicone compound is an alkyl hydrogeno-polysiloxane, for example oo 20 methyl hydrogeno-polysiloxane. o

8. The structural element according to any one of Claims 1 to 7, characterized in the silicone compound represents a proportion by weight of the total dry matter introduced of at least 0.1% and preferably between 0.1 and 1%.

9. The structural element according to any one of Claims 1 to 8, characterized in that the mineral additive has a particle size distribution such that the particles having a size of less than or equal to 63 pm represent a proportion by weight of at least 85 0 s of the said mineral additive.

The structural element according to any one of Claims 1 to 9, characterized in that the mineral additive has a loss on ignition at 900 0 C of less than tvlm M0111546037v3 304670404

11. The structural element according to any one of Claims 1 to 10, characterized in that the mineral additive represents a proportion of the total weight of the ingredients, excluding water, of at least 5% and preferably at most

12. The structural e element according to any one of Claims 1 to 11, characterized in that the mineral additive dispersed in the cured-plaster substrate comprises a clayey material, a crystalline silica and an inert mineral supplement compatible with the clayey material.

13. The structural element according to Claim 12, characterized in that the mineral additive comprises, in approximately equal proportions by weight, the clayey material, the crystalline silica and the inert mineral supplement.

14. The structural element according to any one of Claims 1 to 13, characterized in that the mineral additive comprises dolomite as the mineral supplement.

The structural element according to any one of Claims 1 to 14, characterized in that the composition by weight of the said mineral additive in the dry o matter, in combination with the amount of the water-repellent agent, is ASTM 630/630M-96a standards.

16. The structural element according to any one of Claims 1 to 15, characterized in that the composition by weight of the said mineral additive in the dry 20 matter is tailored also to give the said structural element a fire resistance which meets the German standards DIN 18180 and 4102 (part V) relating to a •c* Sgo• so-called GKF board. oooo

17. The structural element according to any one of Claims 1 to 16, having the .shape of a board, characterized in that the two faces of the cured-plaster substrate are coated with two sheets of cellulose fibres, for example with paperboard.

18. The structural element according to any one of Claims 1 to 17, having the shape of a board, characterized in that reinforcing cellulose fibres are distributed in the cured-plaster substrate, for example a so-called "GFB" fibreboard. tnlm M0111546037v3 304670404

19. The structural element according to any one of Claims 1 to 18, characterized in that mineral fibres compatible with the hydratable calcium sulfate, for example glass fibres, are distributed in the cured-plaster substrate in a proportion by weight of less than 1% of the dry matter.

20. A water-repellent composition, for a substrate based on cured plaster, comprising, as a homogeneous mix, a water-repellent agent comprising a silicone compound, and a mineral additive comprising, on the one hand, a clayey material, which does not swell in aqueous medium and does not have a hydroxyl functional group ionizable in aqueous medium, and, on the other hand, a crystalline silica, the said mineral additive having a synergistic water-repellency affinity with the said silicone compound, in the sense that, by virtue of adding the mineral additive to the water-repellent composition, the water-repellency obtained for the said substrate is increased by at least 20%, in equivalent Cobb, according to the ASTM 630/630M-96a standard, and/or for 15 the same water repellency (or water resistance) the amount of water-repellent agent required is reduced by at least S.i o

21. The composition according to Claim 20, characterized in that the silicone compound and the clayey material are able to form between them, in acid or neutral medium, at least one hydrogen bond between, on one side, the hydrogen of an non ionizable hydroxyl functional group of the clayey material and, on the other side, the oxygen of the silicone compound.

22. The use of a mineral additive, in order to increase the water repellency of a water-repellent agent for a substrate based on cured plaster, comprising a Vsilicone compound, characterized in that the said mineral additive comprises, S: 25 on the one hand, a clayey material, which does not swell in aqueous medium S"and does not have a hydroxyl functional group ionizable in aqueous medium, and, on the other hand, a crystalline silica, the said mineral additive, having a synergistic water-repellency affinity with the said silicone compound, in the sense that, by virtue of adding the mineral additive to the water-repellent composition, the water repellency obtained for the said substrate is increased by at least 20%, in equivalent Cobb, according to the ASTM 630/630M-96a vIm M0111546037v3 304670404 standard and/or for the same water repellency (or water resistance) the amount of water-repellent agent required is reduced by at least

23. A process for manufacturing a structural element comprising a substrate based on cured plaster, in which the said substrate is obtained by at least the following steps: a) dry matter comprising mostly at least one hydratable calcium sulfate, a water-repellent agent comprising at least one silicone compound and water of hydration are homogeneously mixed and this substrate is preformed in the wet state; b) the preformed substrate is dried in order to obtain the substrate formed in the solid and dry state; characterized in that, during step a mineral additive, comprising, on the one hand, a clayey material, which does not swell in aqueous medium and does not have a hydroxyl functional group ionizable in aqueous medium, and, so o 15 on the other hand, a crystalline silica, is also mixed in, the said mineral additive having a synergistic water-repellency affinity with the said silicone compound, in the sense that, by virtue of adding the mineral additive to the water-repellent composition, the water repellency obtained for the said substrate is increased by at least 20%, in equivalent Cobb, according to the 20 ASTM 630/630M-96a standard, and/or for the same water repellency (or water S: resistance) the amount of water-repellent agent required is reduced by at least o. *o

24. The process according to Claim 23, in order to obtain a "GFB" fibreboard, .0 characterized in that the process employed is of the papermaking type with 25 filtration.

The process according to Claim 23 or Claim 24, characterized in that the process comprises a so-called semi-wet or semi-dry compression step.

26. The use of a water-repellent composition according to Claim 20 within a plaster substrate of a prefabricated structural element. tvlm M0111546037v3 304670404

27. A water resistant prefabricated structural element, substantially as hereinbefore described and with reference to Example 3 or Example 4.

28. A water repellent composition, substantially as hereinbefore described and with reference to Example 3 or Example 4.

29. A process for manufacturing a structural element substantially as herein before described and with reference to Example 3 or Example 4. Lafarge Platres 23 July 2004 *o o**o a S *aw e* 0 0 tf tvlm M0111546037v3 304670404